class Calculator:
    def calculate(self, num1, num2, operator):
        result = None
        if operator == "+":
            result = num1 + num2
        elif operator == "-":
            result = num1 - num2
        elif operator == "*":
            result = num1 * num2
        elif operator == "/":
            result = num1 / num2
        else:
            return "Invalid operator"
        return result

calculator = Calculator()
result = calculator.calculate(5, 3, "+")
print(result)  # 8

result = calculator.calculate(5, 3, "-")
print(result)  # 2

result = calculator.calculate(5, 3, "*")
print(result)  # 15

result = calculator.calculate(5, 3, "/")
print(result)  # 1.6666666666666667

result = calculator.calculate(5, 3, "%")
print(result)  # "Invalid operator"
